Spiral spring



(No Model.)

J. LUDLUM.

SPIRAL SPRING;

N0. 303,302 Patented Aug. 12, 1884.

UNITED STATES PATENT Prion;

Janus L'UnLUt on ronr ron, NEW JERSEY.

SPIRAL SPRING.

SPBCIPIGATION forming part of Letters Patent. No. 303,302, dated August12, 1884.

Application filed July 526*. 1883. (No model.)

' To aaZZ whom it may concern.-

cal inner edge was wider than the outer edge;

and spiral springs have been made from bars having one edge thicker thanthe other, so that when rolled edgewise the inner vertical edge would beconsiderably thicker than the outer edge; and springs have also beenformed from a bar rolled against a slightly-thinner inner edge, so thatwhen the spring is coiled said inner edge will flatten out or be leveledand become practically of the same width as the outer edge, theupsettingtending only to spread the metal sufficiently for thispurpose.In these springs the metal was not distributed so as to give the bestworking results.

My invention relates to spiral springs where in the outer edge isthicker than the inner edge, and wherein a section of the spring issimilar to a section of an isosceles triangle, the two equal sides ofwhich angle are form ed by lines drawn or radiating from the exteriorcircumference of the spring on one side across to the other side. Thedivergence of thelines forming these equal sides will depend upon thediameter of the coiled spring and the side of the bar used. I propose toemploy bars for coiling these springs whose cross-sections shall varyaccording to the size and form and similar to the section of anisosceles triangle. The two sides 1 2 are on lines converging to a pointat opposite sides of the spring, the vertical inner edge, a, beingnarrower than the vertical outer edge, of. The edges of the metal Iprefer to round, as shown.

In Fig. 2 I have shown sectionally one spiral spring within another, andthe sections of these springs are companion sections of the sameisosceles triangle, as will be seen by their position and the dottedlines in the said figure; but it is not essential that all the spiralsshall be so formed. Each one may be independent of the other, accordingto the power desired for it.

It is well known that if a steel bar of a given section is coiled into aspring of small diameter it will be stiffer than a spring made from thesame kind of bar when coiled into a spring of larger diameter. Of coursethe small coil of the same length and pitch will not require as long abar as a coil of larger diameter.

In heavy coiled or helical springs for railway-cars, vehicles, &c., thesame condition holds good; The inner edge of the coil is not as long asthe outer edge of the same coil;

and if the inner edge is as thick as the outer edge the inner edge willtake more than its own share of pressure, because the inner edge is thestiffer. For these reasons heavy coiled springs are liable to rupture onthe inner parts of the coil, and the springs are unduly rigid and liableto lose their elasticity, or to give a harsh movement to the vehiclewhen the wheels are exposedv to concussion.

I have discovered that the parts of the metal in coiled springs will alltake their proportionate strain when the steel bar is trapczoidal insectional shape, the converging lines, if prolonged, meeting at apointthat is, a distance corresponding (or nearly so) to the diameter ofthe coil forming the spring. 'VVhen made in this manner, the inner coil(shown in Fig. 2) will require the same force or nearly so) as the outercoil to compress it a given distance, and it will not be liable to bebroken, whereas, if the inner coil were a bar of the same section as theouter coil, it would be much the stiffer and be liable to break. willnow be apparent that if the spring were made of a bar which, when rolledup, was of l rowest edge inwardly, the thickness of the the sectionalshape corresponding to the two coils, Fig. 2, if united, each part ofthe spring would take its proportion of the load. These generalprinciples are applicable to all heavycoiled springs. The bars made useof should .be trapezoidal in section, and the converging sides shouldincline upon lines which, if prolonged, would reach (or nearly so) theopposite side of the coil.

I claim as my invention- A coiled spring made of a steel bar oftrapezoidal sectional form, rolled up with the narmetal at the outer andinner portions being 15 proportioned to the diameter of the spring,substantially as specified, so that each portion of the spring isadapted to take its share of the load, as set forth.

' Signed by me this 17th day of July, A. D. 20 1883.

JA S. LUDLUM.

Witnesses:

GEO. T; PINCKNEY, HAROLD SERRELL.

